Various types of suspension systems for heavy duty trucks, trailers, buses, automobiles and other vehicles are known, and these include: passive systems, active systems, semi-active systems and adaptive systems. The suspension variables in a passive suspension system do not change over time (except through wear), and as a result suspension movement is determined entirely by the road surface and other external factors. In active suspension systems, actuators can exert an independent force on the suspension to improve the ride characteristics. Both semi-active and adaptive suspension systems can vary a property of the suspension, usually damping, to rapidly achieve a better ride, better road-holding, or a combination of the two. Semi-active suspension systems differ from adaptive suspension systems, however, in that the characteristics of the suspension change more rapidly in a semi-active suspension system.
Semi-active suspension systems differ from active suspension systems in that less energy is used in semi-active suspension systems and, in contrast to active suspension systems, no direct force is applied to the suspension system via power input from a control system. Instead, a small amount of energy is used to change the characteristic (e.g., damping) of the suspension system by, for example, electronically varying the size of an orifice through which damping fluid passes. By way of example, in the event the vehicle experiences a shock, a semi-active suspension system can only operate to dissipate the energy from the shock and not to apply an independent force in the same direction as the suspension motion resulting from the shock. Accordingly, semi-active suspension systems use less energy and are thus less costly than active suspension systems, yet they can still provide ride benefits beyond what can be achieved with a passive or adaptive suspension system.
Vehicle height control systems are also well known. A common height control system includes a mechanically actuated height control valve (e.g., a rotary valve) that controls the flow of pressurized air to and from one or more suspension air springs based on suspension motion. Operation of the height control valve can allow air to flow into the air spring to increase the height, or flow out of the air spring to reduce the height, in response to both dynamic events as well as changes in static load on the suspension. Some vehicles include electronic height control systems that operate one or more valves based on input from one or more height sensors. In such systems, dynamic events can be ignored so that the system only adjusts suspension height in response to changes in static load that affect the ride height. This has the benefit of considerably reducing air consumption by the height control system, and thereby improving fuel economy.
Various types of cab mounting suspension systems are known. In one of the most common types used in the United States, the two front corners of the cab are mounted to the vehicle frame with passive rubber isolators, and the rear of the cab is mounted to the frame with either one or two air springs and corresponding shock absorbers. Another common configuration uses rubber isolators at each of the front and rear corners of the cab, or alternatively, rubber isolators at the two front corners and a single rubber isolator at the rear of the cab. Other configurations use air springs or air springs and shock absorber combinations at each of the four corners of the cab.
Many of the suspension control systems available today only address one aspect of vehicle suspension (e.g., damping, ride height, etc.). Additionally, different suspension technologies can be used at the front and rear of the cab, and often each of the technologies is provided by a different manufacturer that provides a particular controller and control solution that is unique to their individual components. These factors prohibit combining multiple technologies in a cost-effective manner to provide a complete cab suspension solution that offers superior performance.